Re: [PATCH] PCI / ACPI / PM: Resume bridges w/o drivers on suspend-to-RAM

[Mika Westerberg]

On Tue, Jun 26, 2018 at 12:06:01PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> It is reported that commit c62ec4610c40 (PM / core: Fix direct_complete
> handling for devices with no callbacks) introduced a system suspend
> regression on Samsung 305V4A by allowing a PCI bridge (not a PCIe
> port) to stay in D3 over suspend-to-RAM, which is a side effect of
> setting power.direct_complete for the children of that bridge that
> have no PM callbacks.
> 
> On the majority of systems PCI bridges are not allowed to be
> runtime-suspended (the power/control sysfs attribute is set to "on"
> for them by default), but user space can change that setting and if
> it does so and a given bridge has no children with PM callbacks, the
> direct_complete optimization will be applied to it and it will stay
> in suspend over system suspend.  Apparently, that confuses the
> platform firmware on the affected machine and that may very well
> happen elsewhere, so avoid the direct_complete optimization for
> PCI bridges with no drivers (if there is a driver, it should take
> care of the PM handling) on suspend-to-RAM altogether (that should
> not matter for suspend-to-idle as platform firmware is not involved
> in it).
> 
> Fixes: c62ec4610c40 (PM / core: Fix direct_complete handling for devices with no callbacks)
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=199941
> Reported-by: n0000b.n000b@xxxxxxxxx
> Tested-by: n0000b.n000b@xxxxxxxxx
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>